This project will develop a CT scanner system which is uniquely suited to the task of providing attenuation cross-section information for the purposes of radiation therapy treatment planning. Patients will be scanned exactly as set-up for their radiation therapy treatment, thus avoiding the distortions introduced by alternative schemes. Full interaction between the CT scanner system and the treatment planning system will be implemented. A display module will be developed to show the CT image and generated isodose distributions in superposition. This CT scanner system will be capable of being duplicated at a low cost compared to commercial CT systems, consistent with the goal of encouraging widespread use of CT scanners for radiation therapy treatment planning.